1. Field of the Invention.
The present invention relates to a unique method of controlling the release profile of materials containing water-soluble components, which has the added advantage of utilizing substantial amounts of waste materials normally having high disposal costs and unfavorable environmental impact. The instant system and process can include production of an agglomerated soluble fertilizer nutrient dispersed in a wax-polymer matrix, which is then coated with an additional wax-polymer film to thereby release the encapsulated nutrient in a predetermined manner. The nutrients which can be used in this type of release mechanism comprise a plethora of water-soluble compounds, primarily those containing nitrogen. Waste disposition situations which would be addressed include, but are not limited to, polyethylene from wire reclamation, wax from investment casting, iron and zinc salts from galvanizing and steel production, and animal litter resulting from feed lot operations and more specifically litter resulting from operation of poultry houses. As used herein, chicken litter, poultry litter or litter means a waste material derived from poultry (chicken) broiler production. It comprises approximately 25 percent chicken feces and 75 percent wood shavings or sawdust. The material is "composted" by wetting and placing in mounds, then aerated periodically to encourage biological activity, with such wetting and aeration being continued until all apparent biological activity has ceased.
An increase in groundwater contamination in many populated areas of the world necessitates more efficient use of nitrogen fertilizers. One means of accomplishing this desired objective would be to produce fertilizers which release their nutrients according to predetermined release rate profiles. Accordingly, as the nutrient is released by a particular fertilizer it would become available for uptake and consumption by the crop for which the fertilizer was specifically designed. The net result would be more nitrogen available to the plant for its use and less "free" nitrogen available for undesirable leaching from the root zone of the soil situs. Slow release fertilizers currently available all offer the same or similar linear release profiles (percent of total nutrient released vs time). Although these fertilizers are adequate for some needs such as turf, they do not offer the release properties needed for major agricultural crops. The present invention offers the capability of manufacturing a fertilizer whose release profile could be predetermined by various matrix/coating combinations, thereby effectively changing or altering not just the slope of a resulting time/release curve but also the shape (order) thereof.
2. Description of the Prior Art
In 1965, a new combination comprising urea, a coating of sulfur (SCU), and a sealant of paraffin oil and polyethylene was reported by Blouin (U.S. Pat. No. 3,295,950, Jan. 3, 1967) which effectively delayed the release of the nitrogen nutrient contained therein. Subsequent patents by Blouin (U.S. Pat. No. 3,342,577, Sept. 19, 1967), Shirley (U.S. Pat. No. 3,903,333, Sept. 2, 1975), and Gullet (U.S. Pat. No. 4,676,821, Jun. 30, 1987) describe improvements or modifications of this process. U.S. Pat. Nos. 3,014,783, Young, Dec. 26, 1961; 3,458,303, Belak, Jul. 29, 1969; 3,400,011, Fox, Sep. 3, 1968; and U.S. Pat. No. 3,314,778, Fox, Apr. 18, 1967, all describe processes or materials for the coating of soluble fertilizer nutrients to delay or control the nutrient release. Hofacker (U.S. Pat. No. 4,002,458, Jan. 11, 1977) teaches the encapsulation of aqueous fertilizer solutions in a wax-polyethylene-hydrocarbon shell. More recently, Chisso-Asahi Fertilizer Co., Ltd. of Japan introduced a series of products coated with polyolefin resins.
From the teachings above, as well as other disclosures in the prior art, it should be appreciated that although coated fertilizer materials as presently produced are effective for some fertilization application needs, they are fraught with a plethora of difficulties and are of limited usefulness due to the following three factors:
1. Since the only barrier to dissolution is the thin coating on the soluble fertilizer, improperly formed coatings or damage to such coatings during manufacture, shipping, or application can result in a "dumping" of a portion of the nutrient. "Dumping" is the immediate release of fertilizer nutrients upon application. Unless the "dumping" of the nutrient is excessive there is usually no harm to crops, but the fertilizer user ends up paying premium rates for that portion of this material which functions like any common water-soluble fertilizer. PA0 2. All mass-produced and currently available coated fertilizer materials, along with a great variety of other water-soluble materials, have a linear release profile (time vs percent of total nutrient released). The release rate is greatest immediately after application and decreases with time. Although this release profile is acceptable for some crops such as turf grass, it is inadequate for most major crops which require small amounts of fertilizer during early growth and large amounts of fertilizer nutrients to be available during periods of rapid plant growth or fruiting. PA0 3. High production costs for most coated fertilizers prohibit their use on major food crops. For instance, the increased cost for applying coatings onto many fertilizer materials can easily range from 300 percent for SCU to as much as 1,000 percent for some polymer-coated material.
The dispersion of soluble nutrients in a hydrophobic matrix has been the subject of study by several researchers including, Hess (U.S. Pat. No. 3,285,733, Nov. 15, 1966), Sommer (U.S. Pat. No. 3,748,115, Jul. 24, 1973), Campbell (U.S. Pat. Nos. 3,290,139, Dec. 6, 1966; U.S. Pat. No. 3,331,677, Jul. 18, 1967; U.S. Pat. No. 3,314,778, Apr. 18, 1967; and U.S. Pat. No. 3,306,728, Feb. 18, 1967), and Malmberg (U.S. Pat. No. 3,306,730, Feb. 28, 1967). More particularly, Hollstein (U.S. Pat. No. 3,300,294, Jan. 24, 1967) and Bozzelli (U.S. Pat. No. 3,300,293, Jan. 24, 1967) teach methods wherein may be produced a variety of fertilizers which are dispersed in petroleum waxes, either with or without additives. Only the teachings of Hollstein supra, are concerned with the use of waxes in combination with polymeric material. More particularly, Hollstein appears to be concerned only with teachings which utilize polymeric materials to thereby allow for formation of wax-urea adducts. It has now been determined that of the fertilizers dispersed in wax-additives, only the wax-polymer formulations, in combination with the wax-urea adduct formation, deter nutrient release enough to be of any practical value for use with most crops. Although Cardarelli (U.S. Pat. No. 4,299,613, Nov. 10, 1981) teaches the use of polymer for his matrix component, his teachings appear to be directed only to the encapsulation of micronutrients and, unfortunately, address neither macronutrient supply nor nonlinear release rates of the type herein proposed.
In view of the prior art teaching supra, and the teaching of the instant new invention as herein discussed infra, it should be appreciated by those skilled in this art that the problems and limitations associated with the direct coating of water-soluble nutrients are now overcome by the practice of the instant invention in which a wax-polymeric coating is applied to particulate fertilizer material which has previously been dispersed in a wax-polymeric matrix rather than being applied to the surface of each particle of the water-soluble nutrient.